Cotton-topped tamarins are small primates with long white hair tufts on their heads. While observing these animals, you notice that males with longer hair mate more frequently and sire more offspring. To test the hypothesis that longer hair is adaptive in these males, you should:A) look for hair in tamarin ancestors B) observe whether shaved males can mate C) determine if hair length is heritable D) investigate if other male traits are adaptive

To test the hypothesis that longer hair is adaptive in cotton-topped tamarins, meaning that it provides some sort of advantage in mating, you should:

C) determine if hair length is heritable.

This is because, for a trait to be adaptive from an evolutionary standpoint, it must meet certain criteria. First, the trait in question (in this case, the long hair tufts) must confer some sort of reproductive advantage to the individuals that possess it. This seems to be indicated by your observations that males with longer hair mate more frequently and sire more offspring. Second, the trait must be heritable ,it must be passed from parents to offspring through genetic means. If the trait of long hair is not heritable, then it cannot be acted upon by natural or sexual selection, and thus the trait's prevalence in the population would not be due to its adaptive value.